The present invention concerns the production of ethanol from cellulosic materials and, in particular, the production of a wort from materials containing cellulose, such as scrap paper, wood or paper pulps, and the subsequent fermentation and distillation of this wort into ethanol. The process described may be implemented by both large and small scale systems in order to obtain favorable economic yields, and this process is particularly suitable for batch-wise production of fermentable wort.
The production of basic sugars from cellulosic materials has been known for some time, as has the subsequent fermentation and distillation of these sugars into ethanol. Much of the prior art development occurred around the time of World War II when fuels were a premium in such countries as Germany, Japan and the Soviet Union. These early processes were primarily directed to acid hydrolysis but were fairly complex in their engineering and design and were very sensitive to small variations in process variables, such as temperature, pressure and acid concentrations. A comprehensive discussion of these early processes, as well as some more modern techniques, is thoroughly presented in "Production of Sugars From Wood Using High-pressure Hydrogen Chloride", Biotechnology and Bioengineering, Volume XXV, at 2757-2773 (1983).
The abundant supply of petroleum in the period from World War II through the early 1970s slowed ethanol conversion research. However, due to the oil crisis of 1973, researchers increased their efforts in developing processes for the utilization of wood and agricultural byproducts for the production of ethanol as alternate energy sources. This research was especially important for development of ethanol as a gasoline additive to reduce the dependency of the United States upon foreign oil production, to increase the octane rating of fuels, and to reduce exhaust pollutants as an environmental measure.
Concurrently with the "oil crisis," as it became known, the Environmental Protection Agency of the United States promulgated regulations requiring the reduction of lead additives in an effort to reduce air polution. Insofar as ethanol is virtually a replacement of lead, some refineries have selected ethanol as the substitute, especially since it can easily be introduced into a refinery's operation without costly capital equipment investment.
In addition to improving the prior high pressure and high temperature HCL gas saccharification processes developed decades ago, current research is directing its efforts primarily in the enzymic conversion processes such as that employed by the University of Arkansas and that being developed by the Massachusetts Institute of Technology. These processes employ the use of enzymes, such as thermophilic organisms (e.g. clostridium thermocellum) which breaks the cellulose into fermentable sugars. Uncertainty still remains with these processes and their ability to be scaled up for commercialization as well as their relatively slow rates of ethanol production. A continuous acid-hydrolysis process is proposed by researchers at New York University wherein a plug of cellulose substrate is injected with steam to break the cellulase and lignin bond. This system has fairly narrow operating tolerances, high energy input and experiences difficulty in being scaled up for commercialization. An acid/methanol process utilizing hot sulphuric acid at a two percent concentration has been developed as the Purdue University/Tsao process, but the commercial viability of this process is still questioned. These prior art processes, as well as many others, are described in a report entitled "Energy from Biological Processes," Congress of the Unites States, Office of Technology Assessment (July 1980).
One of the largest potential sources for "new materials" containing levels of cellulose suitable for conversion into ethanol is waste paper. Although the demand for waste paper used for both recycling and for waste-to-energy programs is increasing, current projections show that at least for the next 20 years, many tons of material will still be collected and disposed at land fills. This is true even through the conversion of waste paper into ethanol is indisputably more economical than land filling due to the cost of waste disposal, particularly land costs and transportation costs associated with land fill operations. In addition to these costs, there are the problems confronted with environmental regulation as well as the aesthetic degradation where a land fill is employed.
Despite the availability of the techniques mentioned above which techniques produce ethanol from cellulosic materials, there remains a need for a simple method for ethanol conversion which takes advantage of low cost equipment and does not consume massive quantities of processing materials, such as mineral acid. There is further need for such a process that may be implemented in both large and small scale operations in order to avoid the uneconomical costs of transporting cellulosic wastes and which avoids the aesthetic cost of land fill operations.